Two forces having magnitude \( A \) and \( \dfrac{A}{2} \) are perpendicular to each other. The magnitude of their resultant is:
\( \dfrac{\sqrt{5} A^{2}}{2} \)
\( \dfrac{5 A}{2} \)
\( \dfrac{\sqrt{5} A}{4} \)
\( \dfrac{\sqrt{5} A}{2} \)